Oxygen Surface Exchange on Stepped (100) Surfaces of Strontium Titanate

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The influence of surface steps on the rate of oxygen surface exchange was investigated for a perovskite-type oxide by means of 18 O 2 / 16 O 2 exchange. Seven vicinal (100)-oriented single-crystal samples of acceptor-doped SrTiO 3 with TiO 2 -terminated surfaces and miscut angles between 0 and 3° were used, giving a variation in step density (ρ st ) of a factor of approximately 7. All samples were subjected together to a single high-temperature isotope exchange anneal (at T = 1023 K in p O 2 = 0.1 bar, with p H 2 O < 10 –7 bar) and were then analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). Numerical descriptions of the isotope diffusion profiles yielded the oxygen tracer diffusion coefficient for the bulk ( D *), the oxygen isotope exchange coefficient for the surface ( k *), and the space-charge potential at the surface (Φ 0 ). Surprisingly, the k * data exhibited no increase with increasing ρ st, suggesting that surface steps do not strongly promote oxygen surface exchange in this system under these conditions. The behavior of Φ 0 as a function of ρ st is consistent with preferential formation of oxygen vacancies both at under-coordinated oxide-ion sites of terraces and at under-coordinated oxide-ion sites of step edges and terraces.